Method for the production of an ice surface for ice rinks

ABSTRACT

A method for producing an ice surface for an ice rink by freezing water to which an inorganic substance is added is characterized in that the inorganic substance is ammonia, an alkali hydroxide or alkaline earth hydroxide, a hydrogen halide, nitric acid, sulfuric acid, phosphoric acid, an alkali salt, alkaline earth salt or ammonium salt of said acids, or ammonium-bicarbonate, or a mixture of several of said substances.

The invention starts out from a method for the production of an ice surface for an ice rink in accordance with the preamble of claim 1.

The ice quality of an ice rink plays a central role particularly for speed competitions, e.g., speed skating. The mechanical properties of the ice, correspondingly, of the ice surface of the ice rinks, can be controlled via various parameters, e.g. via the ice temperature, the relative atmospheric humidity or the conductivity of the water forming the ice.

Various methods for improving the ice quality are known so far. Mechanical unevenness or contaminations in the ice are flattened or removed by ice resurfacing machines. In order to control air temperature and humidity, ice rinks are installed in ice pavilions. It is furthermore known to remove bothersome sodium and calcium ions from the ice by means of desalination and decalcification using an osmosis system. Also known is the use of de-ionized water instead of mineral-containing tap water during ice preparation for minimizing the friction caused by the ions in the water.

Also the addition of various organic or inorganic substances to the water before the freezing process is known. For example, from the patent document DE 526 224 it arises that the surface area to be iced is covered with a salt mixture of sodium carbonate and sodium sulphate, which is admixed with water until the salt reaches a state of maximum content of water of crystallization, and the mixture is frozen thereafter.

Disadvantages related to the known methods of improving ice quality, particularly to the methods of osmosis and demineralization, are the high costs of installation and maintenance.

Thus it is the object of the invention to disclose a cost-efficient method for improving the quality of ice for ice rinks.

This object is achieved by means of the characterizing features of claim I together with the category-forming features.

According to the present invention it is provided that a substance is admixed to the ice-forming water, said substance being ammonia, an alkali hydroxide or alkaline earth hydroxide, a hydrogen halide, nitric acid, sulfuric acid, phosphoric acid, an alkali salt, alkaline earth salt or ammonium salt of said acids, or ammonium-bicarbonate, or a mixture of several of said substances.

Thereby it is feasible to accelerate or to retard the freezing process, to obtain selectively a hard or soft, a mechanically resistant, a highly slippery or rather sticky ice surface, which can be prepared and maintained in a simple manner on existing ice rinks using conventional equipment for preparing the ice surface without the need of costly installations or of subsequent installation of expensive equipment.

Further advantageous features and embodiments are evident from the dependent claims.

Advantageously, NH₃, HF, HCl, HBr, HI, NH₄I, NH₄F, NH₄Br, LiOH, NaOH, KOH, Ca(OH)₂ or a mixture of several of these substances are added to the water preferentially, since said substances, due to their physical-chemical properties, cause the strongest effect of all possible dopants.

Furthermore it is advantageous that the substance added to the water is added in a concentration of up to 5 ppm, which requires only small amounts of dopants and is thus cost-efficient.

It is advantageous, furthermore, that the maximum concentration of the substance added to the water does not exceed 20 ppm, since thereby an environment-friendly and—with respect to contamination by possibly noxious substances—safe concentration is ensured.

It is advantageous that the substance added to the water can be added by admixing to the water before freezing in the form of dilute solutions so that a homogeneous ice layer can be generated.

It is also notably advantageous that the substance added to the water can be added after freezing by treating the ice with a liquid which contains the additives because thereby also an ice surface which was prepared using un-doped water can be improved in terms of quality afterwards during post-processing of the ice surface, without the need of freezing a new ice surface from scratch.

For the preparation of ice for speed competitions such as for example speed skating, it is desirable to reduce the coefficient of friction of the ice surface. Up to now, mainly an optimization of factors in the surroundings of the sportspersons has been carried out, e.g. the athlete's clothing (thin, aerodynamic skins as a suit or long, thin blades on the skates) or a reduction of the air drag by relocating the ice rinks into sports halls or to high altitudes. As recently as in the past 10 years one has begun to consider also the ice itself in order to achieve an improvement of the surface of the ice and therewith increased velocities.

The fact that a quasi-liquid layer on the ice causes its known properties (slippery, etc.) has been known since Faraday in 1850. The dependence of the thickness of this thin water film on temperature is the result of various studies performed within the last 50 years. Below approx. −25° C. this water film disappears, and the ice becomes “sticky” (tongue sticks to ice, etc.). The novelty of the present invention consists in that the layer thickness and therefore the properties of the ice can be governed towards the desired direction, for instance towards a lower coefficient of sliding friction, at any arbitrary ice temperature by means of specific addition of admixtures at trace concentrations.

The method according to the present invention thereby proposes for the production of ice by freezing of de-ionized water, to add admixtures purposefully to said water, i.e. to dope the water. This brings about that properties such as the static as well as the dynamic coefficient of friction or the surface hardness can be selectively controlled by these additives. The additive can either be added by admixing it to the water (before freezing) in the form of dilute solutions or by treating the ice (after freezing) with a liquid which contains the admixtures. An adaption of currently used ice preparation machines is not necessary, since instead of water simply contaminated water, e.g., de-ionized water, tap water, distilled water, etc. can be used.

In the following the method according to the invention is illustrated on the basis of the execution of the method using a preferred admixture.

As an example, the doping of water with 4 ppm NH₃ is described here. In order to prepare an ice surface of 200 m² and 5 cm thickness, 10000 litres of water are needed. These are typically sprinkled onto a pre-cooled area using a hose, which is connected to the water pipe. A uniform doping with NH₃ can e.g. be achieved by interconnecting a metering valve which doses a dilute NH₃ solution into the tap water in dependence on the rate of flow. One e.g. provides one litre of a 4% solution of NH₃, which is supposed to be dosed into the water. At a flow rate of 50 litres per minute the metering valve is supposed to dose in 5 millilitres per minute for a duration of 200 minutes. This results in a dilution of 1:10000 so that the tap water finally contains 4 ppm NH₃.

Now the ice needs to be given the time to freeze homogeneously on the pre-cooled surface. For this purpose the protocols can be employed which are used by ice preparation specialists today. The more time the ice is given, i.e., the slower the cooling rates, the larger the crystals and the smoother the ice surface. If one cools faster, then smaller crystals result which abut upon each other and produce interfaces (“triple junctions” or “grain boundaries”, respectively)—the ice surface becomes rough.

The method is also suitable for a surface treatment of the ice using special ice preparation machines. These machines, which are for instance employed during the breaks in ice hockey matches, mostly have a water tank and a snow container. These machines collect abraded snow, fine down the topmost ice layer and apply a new layer of water onto the ice. If one mixes an appropriate amount of NH₃ also into the water tank of the machine, then previously un-doped ice benefits for the first time from the surface properties improved by the doping, or, correspondingly, in case of ice which has already been prepared by means of doping, the optimized properties of the doped ice persist even after repeated ice preparation.

By the selection of the dopant or alternatively of the dopant mixture and of the mixing ratios various ice properties can be optimized:

For example, 3 ppm HF bring about a considerable increase in the ice flow properties. An ice-skater “cuts” into the ice with his blade and thereby displaces ice from the groove, which normally ends up as “snow” on the ice surface. In the case of doping with 3 ppm HF, the displaced ice flows back into the (just produced) groove to a much greater extent so that firstly less “snow” comes to lie on the ice surface and secondly the degree of destruction of the ice surface is minimized. In parallel with this, the ice surface also becomes softer. Using 3 ppm NH₃ instead, the opposite effect occurs, attrition is enforced, the ice surface gets destroyed more severely and also becomes harder.

If one needs a very hard ice surface (e.g., for ice hockey matches), then NH₃ doped ice has a decisive advantage: Today, ice preparation specialists adjust the ice hardness via the temperature. Soft ice surfaces (e.g. for figure skaters) are produced by making “warm” ice (e.g., at −3° C.), while hard ice surfaces require cooling to e.g. −10° C., thereby consuming much energy. Using NH₃ doped ice one can produce harder ice already at higher temperatures in an energy-saving manner.

For organizers of major speed skating events it is furthermore of great importance that national and continental or even Olympic and world records are run on their tracks. Ice from which one can push off better and on which one glides better, is very important here. The method according to the invention is also suitable for controlling the coefficient of sliding friction. For instance it can be measured that a certain doping results in a water film even on an ice surface at −80° C., which reduces dynamic friction. On un-doped ice this water film disappears already below approx. −25° C. so that cryogenic ice is no longer slippery. It is also conceivable that a dopant is found which increases dynamic friction on ice strongly by suppressing the water film already at comparably high temperatures.

Good ice surfaces are prepared over a period of several days, since this is the time needed to extract the thermal energy from the water molecules, to produce crystallization nuclei and to achieve optimum crystal growth. Doping with a suitable additive can accelerate all three of these processes and, therefore, can reduce time and costs for producing an ice surface.

The investigated substances are built directly into the ice lattice up to concentrations of 5 ppm and change the microscopic properties such as relaxation times, H-transfer times, electric conductivity, etc. via the production of so-called D- or L-defects. This leads to a change of the macroscopic properties. Other substances such as for example bigger inorganic molecules, organic molecules, etc. are not built into the crystal lattice, but merely into lattice voids or grain boundaries, in many cases they are even only discharged via the surface and, accordingly, do not alter the microscopic and macroscopic properties of ice.

The list of substances that are capable of being built into the crystal lattice and which are therefore suitable for doping comprises ammonia, alkali hydroxides and alkaline earth hydroxides, hydrogen halides, nitric acid, sulfuric acid, phosphoric acid, alkali salts, alkaline earth salts and ammonium salts of said acids, and ammonium-bicarbonate. Particularly preferred are thereby NH₃ (ammonia), HF, HCl, HBr, HI, NH₄I, NH₄F, NH₄Br, LiOH, NaOH, KOH, Ca(OH)₂ or mixtures thereof, which have the highest potential and the maximum effect, respectively.

The range of concentrations which has to be covered results from the concentration of molecules directly (substitutionally) incorporated into the lattice plus from the minerals already present in the tap water. The threshold for fluorides, for example, amounts to 1.5 ppm so that for a hard NH₃-doped ice surface the softening effect of fluorides has to be compensated at first. The maximum of 1.5 ppm for compensation plus 5 ppm which are substitutionally incorporated at the utmost result in a threshold of 6.5 ppm for doping the tap water. Including a safety margin, the maximum concentration which has an influence on the macroscopic ice properties is 20 ppm.

An equivalent amount of the proposed substances is also found in rainwater so that toxicity has not to be assumed. After thawing the ice surface, the disposal of the water containing the additives can be carried out in a simple and cost-effective manner via the canalization. 

1. Method for the production of a homogeneous ice layer for an ice rink by means of freezing water to which an inorganic substance is added, characterized in that the substance added to the water is an alkali hydroxide or alkaline earth hydroxide, a hydrogen halide, nitric acid, sulfuric acid, phosphoric acid, an alkali salt or alkaline earth salt of said acids or a mixture of several of said substances.
 2. Method for the production of hard ice for an ice rink, wherein water is applied to the cooled area of the ice rink, characterized in that ammonia is added to the water before freezing.
 3. Method according to claim 1, characterized in that preferentially HF, HCl, HBr, HI, LiOH, NaOH, KOH, Ca(OH)₂ or mixtures of several of these substances are added to the water.
 4. Method according to any of claims 1 to 3, characterized in that the substance added to the water is added in a concentration of up to 5 ppm.
 5. Method according to claim 1, characterized in that the maximum concentration of the substance added to the water does not exceed 20 ppm.
 6. Method according to claim 1, characterized in that the substance added to the water is added by admixing to the water before freezing in the form of dilute solutions.
 7. Method according to claim 1, characterized in that the substance added to the water is added by treating the ice after freezing with a liquid which contains the additives. 